The invention relates to an apparatus for measuring the angle of rotation in accordance with the preamble of claim 1.
Instruments for measuring angles, also called rotational transducers or encoders, have a housing for the actual angle sensor and a flange on which a stator coupling connects to the housing of a drive system that is to be measured. A shaft coupling, preferably a fixed coupling such as a threaded connection, connects a shaft of the rotational transducer, also called input shaft or encoder shaft, to a drive shaft that is to be measured.
In addition to the needed mechanical interfaces, the rotational transducer has a scale which carries angular position measurements for detection by a sensor that generates position signals. The signals are sent to a signal and data processing unit and they are transmitted via an electric interface to a control unit such as a motor regulator or control. Such rotational transducers can use optical, magnetic, inductive or potentiometric technologies.
The already mentioned stator coupling provides a non-rotatable or fixed connection between the drive system and the rotational transducer. This involves a rotationally fixed coupling of the housing of the rotational transducer to a housing of the drive system to avoid errors in measuring the angle. Preferably the angle measurement error caused by the stator coupling is less than the measurement accuracy of the rotational transducer.
In addition to the measurement of angles, the stator coupling can also be used to couple instruments for measuring other mechanical values, such as the angular velocity, the angular acceleration or torque. The stator coupling functions as a torque support and permits axial and radial shear movements but not rotational movements.
A variety of stator couplings made of metal as well as other resilient materials are known. DE 89 15 109U and DE 100 22 555 A1 describe couplings with connecting elements that define a parallelogram. For this, four bars which are each offset 90xc2x0 from each other are arranged on a material with a high degree of fatigue strength. The stator of the drive system and the rotational indicator housing are secured to opposed bars, that is, bars which are offset with respect to each other by 180xc2x0.
When space is limited, the installation of such systems is difficult because the individual components, namely the rotational transducer with its encoding shaft, the drive system with its housing (stator) and drive shaft, and the stator coupling, must be connected to each other. DE 32 06 875 A1 and DE 33 01 205 A1 describe a stator coupling that is located inside the housing of the rotational indicator. However, such arrangements require a relatively large space.
It is an object of the invention to provide an instrument for measuring angles of rotation which has a stator coupling between the housing of the rotational transducer and the housing of the drive system (drive housing) which prevents angle measurement errors and facilitates the assembly and installation of the rotational transducer on the drive housing.
This object is solved in accordance with the invention with the arrangement set forth in the characterizing portion of claim 1.
In accordance with the invention, the instrument for measuring angles has at least one locking mechanism which non-rotatably connects the encoder shaft and the rotational transducer housing when the rotational transducer and the stator coupling are separated from the drive housing and which frees the encoder shaft when the stator coupling is secured to the drive housing. In this manner, the rotational transducer can be installed on the drive housing by initially threading together the encoding shaft and the drive shaft of the drive system by simply turning the transducer housing because the stator coupling non-rotationally connects the encoding shaft and the transducer housing. Thereafter the stator coupling is secured to the stator of the drive system, which is typically formed by the drive housing. In accordance with the invention, the locking mechanism becomes disengaged and the encoding shaft becomes unlocked. To establish the non-rotational shaft connection, no special tools are needed for engaging the rotational transducer. The shaft connection can be established by simply grasping the entire transducer housing, which is simpler, faster and therefore less costly. In effect, the housing of the rotational transducer forms the tool for connecting the shafts. Additional advantages attained with the present invention are that while connecting the shafts a rotationally fixed stator coupling is provided. Beyond that, the apparatus for measuring rotational angles constructed in accordance with the invention, and in particular the stator coupling, require little space. A problem-free and very precise transmission of the angle is possible, while relative longitudinal and transverse movements of the housings connected by the stator coupling are compensated for.
This arrangement is especially advantageous for small rotational transducers which require installation in limited spaces. By prestressing the stator coupling prior to its installation, the invention provides the additional advantage of a higher resonance frequency for the coupling cooperating with the rotational transducer.
In a further development of the invention, the locking mechanism is defined by a noncircular shoulder on the encoding shaft, which, for locking, extends into a corresponding cut-out of the stator coupling. The lock is engaged by simply extending the shoulder of the encoding shaft into the cut-out. The encoder shaft can be separated equally simply by pulling the stator coupling from the encoding shaft.
The stator coupling preferably has a mounting plate which forms the cut-out and which is preferably connected to a torque support. The mounting plate serves to secure the stator coupling to the stator of a drive system, that is, the drive housing. The torque support is secured to the mounting plate and the housing of the rotational transducer. Securing the mounting plate to the drive housing causes the mounting plate to be pulled off the noncircular shoulder of the encoding shaft, which permits the latter to rotate. This requires a deformation of some regions of the torque support. Consequently, the torque support is preferably made of spring elastic material and defines a radially and axially resilient mechanical connection of the transducer housing and the drive housing.
By providing the torque support with at least one tensioning element, which secures the mounting plate to the rotational transducer when the latter is not installed, and which is deformable against the tension force when the mounting plate is installed on the drive housing, the tensioning element, and not the actual torque support, becomes deformed. This is particularly advantageous because the torque support is constructed to adapt it to the encountered conditions. The torque support is therefore preferably made in the form of a spring parallelogram. For this purpose, two bars are arranged opposite each other and offset by 180xc2x0 on a connecting spring sheet. The bars include connecting elements for connection to the mounting plate and therewith to the drive housing. Two further bars, which are offset with respect to the former by 90xc2x0 each, form a rotationally fixed connection of the transducer housing.
The stator coupling is constructed as a resilient connecting element which has a frequency at which it resonates. To avoid this condition, the resonance frequency should be as high as possible so that the rotational speeds encountered during use of the instrument lie below the resonance frequency. If D is the spring constant of the stator coupling and J the moment of inertia, the resonance frequency f is given as   f  =            1              2        ⁢        π              ⁢                            D          J                    .      
To render the deformation reversible and permit repeated installation of the rotational transducer and the stator coupling, the torque support is made from a spring elastic material, for example spring steel or rubber. The mounting plate is therewith movable in the axial direction.
In a simple embodiment of the invention, the mounting plate is threadably connected to the drive housing.
To facilitate the turning of the transducer housing during installation, it is preferable to form its exterior so that it can be grasped with a tool for turning the transducer housing and to thereby thread the encoding shaft onto the drive shaft.
A further development of the invention prevents the transmission of the entire torque through the torque support when turning the transducer housing during installation. This is effected by providing at least one shoulder on the end of the transducer housing facing the stator coupling and which extends into the cut-out. As a result, the transducer housing and the mounting plate are non-rotatable with respect to each other while the transducer is installed on the drive housing.
To assure that the shafts are securely connected to each other, the ends of the encoding shaft and the drive shaft have respective inner and outer cones.